Conventionally, the image sensor used in the digital still camera or the camera of cellular phone employs the Charge Coupled Device (abbreviated as CCD) or Complementary Metal-Oxide Semiconductor (abbreviated as CMOS). The output data of the image sensor is the image data with the line-based manner. However, if the image format of Joint Photographic Experts Group (abbreviated as JPEG) is served as image data compression and the data compression of JPEG is operated by the block-based manner, e.g. a scanning block of 8*8 pixels for compressing the image data. Therefore, it is required to perform an additional processing step to allocate the image data between the step of output data of the image sensor and the step of data compression of JPEG.
FIG. 1 is a schematic block diagram of a conventional image data processing device 100. The image data processing device 100 includes a writing controller 102a, a reading controller 102b and a buffer 104 having a first buffer area 104a and a second buffer area 104b. The capacity of the first buffer area 104a is equal to that of the second buffer area 104b wherein the first buffer area 104a and the second buffer area 104b have eight lines respectively which require the capacity of sixteen line buffers. The writing controller 102a receives the image data from the image sensor (not shown) and the image data includes the data structure “H*V” pixels wherein “V” indicates the column amount and “H” indicates the pixels in each column of column amount “V”. The image data are written into the first buffer area 104a of the buffer 104 from left line to right line and from top portion to bottom portion. When the first buffer area 104a is fully written, the writing step is witched from the first buffer area 104a to the second buffer area 104b. Further, while the reading controller 102b reads the image data from the first buffer 104a and outputs the image data to the JPEG encoder 106, the reading unit is defined as the block having the “8*8” bytes and the image data stored in the first buffer area 104a are read the from left line to the right line and from top portion to bottom portion for transmitting the reading image data to the JPEG encoder 106 to be compressed. When the second buffer area 104b is fully written, the status of the second buffer area 104b is changed from the writing status to the reading status so that reading controller 102b controls the reading procedure of the second buffer area 104b. When the first buffer area 104a is fully read, the status of the first buffer area 104a is changed from the reading status to the writing status so that the writing controller 102a controls the writing procedure of the first buffer area 104a. 
Based on the above-mentioned descriptions, the image data processing device 100 utilizes many buffers 104. Consequently, there is a need to develop a novel image data processing method to solve the aforementioned problems.